Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

TRADIGRADE

Tardigrades, a.k.a. water bears… there’s just something lovable about them. They’re kind of cute for microorganisms (or kind of horrifying, depending on which picture you’re looking at). And they’re absurdly tough. They can survive almost anything. They can even survive in space.

There have been several experiments now where tardigrades were taken to low Earth orbit and exposed to the vacuum of space for prolonged periods of time. Most of them survived the experience. In the absence of food, water, or oxygen, tardigrades can enter a state of suspended animation, and their cells have the ability to repair their D.N.A. if it gets damaged by solar or cosmic radiation.

In fact tardigrades seem to be so well adapted to the hazards of space that it’s sometimes suggested (usually not by serious scientists) that these little guys might come from space.

German pastor and zoologist Johann August Ephraim Goeze is credited with discovering tardigrades in 1773. Goeze called them Kleiner Wasserbär, which is German for “little water bear,” because the way they walk on their eight pudgy, little legs reminded Goeze of the plodding movements of bears.

In 1777, Italian biologist/Catholic priest Lozzaro Spallanzani made further observations of these creatures. Spallanzani called them il Tardigrado, meaning “slow walker,” again because of the slow, plodding manner in which they walk. The English words tardy and tardiness are closely related, etymologically speaking.

Today we’ve retained both tardigrade and water bear as common names for these creatures. Apparently some people also call them moss piglets, which is just adorable. Over a thousand species of tardigrade have been identified, all classified under the phylum Tardigrada.

As for the question about where tardigrades came from—are they native to this planet, or did they immigrate to Earth from someplace else?—I can only say this: if tardigrades do have an extraterrestrial origin, they must have arrived on Earth a very, very long time ago. The oldest known tardigrade fossils date back to over 500 million years ago (meaning they may have been here since the Cambrian explosion).

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

BIOGENIC

A passing alien spacecraft has been observing our little, blue planet for two weeks now, and it’s time they reported their findings back to their homeworld. One word—one scientific term—will feature prominently in their report: biogenic.

Actually, it’ll be the word xygjaflubozux, but that roughly translates into English as biogenic. It’s an adjective meaning “generated by biological processes.”

It’s difficult to impossible to directly detect life forms on a distant planet, so instead good astro-scientists go looking for chemicals that may have biogenic origins.

In the case of Earth, the aliens report they’ve detected an alarming amount of oxygen in the atmosphere. Oxygen is such a highly reactive chemical that it’s hard to imagine how it could persist in a planet’s atmosphere over long periods of time, unless….

Then there’s methane (which we never talked about in this series… oops). The presence of methane is even harder to explain, because methane reacts so readily with oxygen. All that methane should oxidize away within fifty years, unless….

Could it be biogenic oxygen? Biogenic methane? What about some of the other strange chemicals in Earth’s atmosphere, like nitrous oxide? Could there be biological processes at work constantly replenishing these chemicals in Earth’s atmosphere? These questions will be debated among the alien scientific community for many standard cycles to come.

The only unambiguous evidence of life on Earth, from the aliens’ perspective, were those radio signals coming from the planet’s surface. In a sense, you might say these signals have a biological origin, though I doubt human astro-scientists would describe them as biogenic radio emissions. But maybe the word xugjaflubozux has a slightly broader flavor of meaning and could still apply (how should I know? I don’t speak alien!).

This is the final post for my “Alien Eyes on Earth” series. The aliens have to move on and explore other star systems, but something tells me they’ll be back.

Today’s post was inspired by a 1993 paper by Carl Sagan and others. Sagan and his colleagues wanted to know which of Earth’s features can be observed by a passing spacecraft and, perhaps more interestingly, which features cannot.

Right now, as you read this, our world is being watched keenly and closely by a nearby alien spacecraft. So far the aliens have only observed circumstantial evidence of life: water, oxygen, and a mysterious light-absorbing chemical (chlorophyll). But the aliens are about to detect something that will prove conclusively not only that there’s life on Earth but that there is intelligent life.

Okay, the content of Earth’s radio broadcasts might not seem all that intelligent, but the existence of such broadcasts is clear, unambiguous evidence of a technologically advanced civilization of some kind.

First off, these radio signals are being affected by Earth’s ionosphere in a particularly telling way. During the day, the ionosphere becomes energized by solar radiation, effectively blocking the planet’s radio emissions from escaping into space. But at night, the ionosphere calms down and allows more radio signals through. Because the aliens detect most of the radio emissions from the night side rather than the day side, it would seem clear to them that the signals originate on the planet’s surface, rather than sources near or directly behind the planet.

Secondly, the radio emissions remain stable at constant frequencies over the course of many hours. Naturally occurring radio emissions would tend to drift significantly from one frequency to another over that time period. This strongly suggests an artificial source.

And thirdly, these signals exhibit “pulse-like amplitude modulation”—in other words, the signals appear to be modulated in such a way as to contain bits of information. I imagine this would present something of a double challenge for the aliens: first the technical challenge of decoding the signals, and then the linguistic challenge of interpreting our language—or rather, our many languages.

Whether or not the aliens could make any sense out of these radio signals, this sort of pulsed amplitude modulation is never observed with naturally occurring radio sources. The only reasonable hypothesis is that there is intelligent life on the planet’s surface.

Tomorrow, in the final post for this “Alien Eyes on Earth” series, the aliens will report their findings back to their home planet, and there’s one word—one particular scientific term—that will feature prominently in that report.

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Today’s post was inspired by a 1993 paper by Carl Sagan and others. Sagan and his colleagues wanted to know which of Earth’s features can be observed by a passing spacecraft and, perhaps more interestingly, which features cannot.

P.S.: Of course the aliens would pick up more than just pop music. They’d be able to hear our news, educational programming, personal cell phone calls, coded military transmissions, et cetera, et cetera… but something tells me that music in particular would draw their interest. The special combination of mathematics and aesthetics is, in my opinion, one of the strongest indicators of intelligent life.

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

PHOTOSYNTHESIS

This post is mainly for my extraterrestrial readers, especially you extraterrestrials who are observing Earth from a distance and are a little puzzled by what you’re seeing.

By now, you’re aware of Earth’s active water cycle, and you’ve observed an alarming amount of oxygen in Earth’s atmosphere. You may have also noticed there’s a strange chemical spread across Earth’s landmasses, a chemical that absorbs red light.

This chemical also absorbs blue light, but due to an atmospheric scattering effect, the blue absorption signature might not be easy for you to see. Also, there’s more of this hard-to-identify chemical in Earth’s oceans, but between the atmospheric scattering of blue light and water’s ability to absorb red, you probably can’t detect it.

I realize you aliens must be pretty advanced. I mean, you’ve developed interstellar travel, after all. Even so, I bet you’re struggling to identify this strange chemical substance. Let me help you out: it’s a weird, complicated molecule we humans call chlorophyll, and it’s used in a biochemical process we call photosynthesis.

Here on Earth, photosynthetic life forms like plants, algae, and cyanobacteria use chlorophyll to absorb sunlight (specifically the red and blue wavelengths). This light energy is then used for a sort of carefully controlled photolysis of water and carbon dioxide molecules, which are then recombined to make carbohydrates.

Please note: there are alternative versions of photosynthesis here on Earth that do not require chlorophyll. It’s just that these alternatives aren’t very popular. Haven’t been for over two billion years. This despite the fact that chlorophyll-based photosynthesis produces an extremely hazardous byproduct: oxygen. But hey, at least now you know where Earth’s mysterious oxygen atmosphere comes from!

You probably have something like photosynthesis back on your home planet, but I imagine the details must be different. Some other chemical probably does the job chlorophyll does here on Earth. Whatever your planet’s photosynthetic chemical is, I bet we humans would have a really hard time identifying it… just as you guys were struggling to identify Earth’s chlorophyll.

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Today’s post was inspired by a 1993 paper by Carl Sagan and others. Sagan and his colleagues wanted to know which of Earth’s features can be observed by a passing spacecraft and, perhaps more interestingly, which features cannot.

If an alien spaceship were passing by, there are several things the aliens would notice about Earth, even from a distance. Water, for one thing. And not just any old water, but water in solid, liquid, and gaseous phases. And if that weren’t enough to grab the aliens’ attention, a spectrographic analysis of the atmosphere would reveal another big surprise: oxygen. Alarmingly high quantities of oxygen.

We humans are used to thinking of oxygen as a good thing, something beneficial to life. From an alien perspective, that may not be so. Imagine if I told you about a planet with a 20% chlorine atmosphere. Would you want to go there? Probably not. Chlorine is a highly reactive, extremely toxic chemical. It’s an oxidizer. One of the strongest oxidizers on the periodic table.

But as you could probably guess from the name, oxygen is also a really strong oxidizer—almost as strong as chlorine. We humans have evolved in an oxygen-rich environment. We’re used to it, and we’ve adapted to it so well that oxygen has become a benefit to us rather than a liability.

To extraterrestrials, however, a 20% oxygen atmosphere could be as frightening as a 20% chlorine atmosphere would be to us.

So where does all that oxygen come from? The aliens already know about Earth’s water, so they might speculate about water molecules being broken apart by UV radiation from the Sun. This process, known as photolysis, would turn water (H2O) into atomic hydrogen and atomic oxygen, which could then recombine to make molecular hydrogen (H2) and molecular oxygen (O2). Light-weight hydrogen molecules would then escape to space and be swept off by the solar wind, leaving the heavier oxygen molecules behind.

That might account for some of Earth’s oxygen, but Earth has a lot of oxygen. A lot more than can be explained by photolysis alone. So how can there be so much oxygen? What keeps all that highly reactive oxygen from reacting itself away… unless something is constantly replenishing Earth’s oxygen supply?

These aliens observing our planet are good scientists, so they won’t jump to conclusions too quickly. It’s possible, the aliens might say to each other, that all this oxygen is being generated by biological activity. But they can’t know that for sure. Not yet.

Tomorrow on Sciency Words, we’ll look at a scientific term that you have almost certainly heard of before, but that the aliens maybe haven’t.

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Today’s post was inspired by a 1993 paper by Carl Sagan and others. Sagan and his colleagues wanted to know which of Earth’s features can be observed by a passing spacecraft and, perhaps more interestingly, which features cannot.

Aliens are naturally curious about Earth, once they notice it’s there. Earth is covered in water. That by itself isn’t so unusual, but even from a great distance it’s obvious there’s something special about Earth’s water.

Hydrogen and oxygen are the #1 and #3 most common elements in the universe, respectively; therefore, it shouldn’t surprise anyone that H2O, the simplest hydrogen/oxygen compound, is abundant throughout the cosmos.

In a gaseous form, water is often present in the atmospheres of gas giants. Solid water can be found on many asteroids and comets, as well as on icy worlds like Pluto, Titan, or Europa. Liquid water sometimes exists beneath the surfaces of these icy worlds, and it’s sometimes found on rocky worlds like Mars, typically with salt or other impurities mixed in to help lower its freezing point.

But any passing spaceship observing Earth would notice evidence not just of water, not just of liquid water, but clear evidence of water in all three phases.

Gaseous water: the characteristic absorption lines of water vapor can be detected in a spectrographic analysis of Earth’s atmosphere.

Liquid water: and then there are specular reflections—glints of sunlight reflecting off very smooth surfaces, surfaces so smooth that they almost certainly must be liquid.

It would be one thing to have liquid water sitting stagnant on the planet’s surface, but Earth’s water appears (even from a distance) to be cycling through multiple phase transitions. Passing aliens might not know what that means, but it’s certainly strange enough to make them curious about Earth. Perhaps curious enough to come take a closer look.

* * *

Today’s post was inspired by a 1993 paper by Carl Sagan and others. Sagan and his colleagues wanted to know which of Earth’s features can be observed by a passing spacecraft and, perhaps more interestingly, which features cannot.

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:

THE FERMI PARADOX

Enrico Fermi was an Italian physicist, one of the many great scientists who immigrated to the United States right before the outbreak of World War II. He is most noted for creating the first nuclear reactor and the role he played in the development of the atomic bomb.

But that’s not what we’re going to talk about today. Today we’re talking about something Fermi said half-jokingly over lunch.

Where Is Everybody?

Based on some historical detective work, we can say this probably happened in the summer of 1950. Fermi was visiting the Los Alamos National Laboratory. He and a few colleagues were having a lunchtime conversation about flying saucers. Apparently there had been an amusing cartoon about little green men in a recent edition of the New Yorker.

The conversation got serious (sort of) when Fermi suddenly asked: “but where is everybody?” Everyone at the table laughed, but Fermi’s question and the not-entirely-serious discussion that followed would become the basis of what we now call the Fermi paradox.

As a matter of statistics and probability, it seems like advanced alien civilizations should be out there somewhere. There are over 100 billion stars in our galaxy. Many (if not most) of these stars have planets orbiting them. Some of these planets must surely support life, and in at least a few cases intelligent life—life capable of developing interstellar travel.

Even without faster-than-light technology, one or more of these space-faring civilizations could conceivably spread across the whole galaxy in just a few million years. The galaxy is far, far older than that. There’s been plenty of time for the aliens to do it. So where is everybody? Shouldn’t we have heard from somebody by now?

Or so Fermi argued over his club sandwich (or whatever he was eating) in a half-serious conversation about flying saucers. Of course there are plenty of objections to Fermi’s line of reasoning here, but I’m not going to weigh in on that. Not today. I’m saving my opinion for Monday’s post.